Remove left-out of standard_gatk_options macro.

This was causing the following error:

Traceback (most recent call last):
  File "/opt/shed_tools/central/toolshed.g2.bx.psu.edu/repos/iuc/gatk2/f760c0de8e3a/gatk2/gatk2_wrapper.py", line 138, in <module>
    __main__()
  File "/opt/shed_tools/central/toolshed.g2.bx.psu.edu/repos/iuc/gatk2/f760c0de8e3a/gatk2/gatk2_wrapper.py", line 96, in __main__
    gatk_filename = gatk_filename_from_galaxy( filename, galaxy_ext, target_dir = tmp_dir, prefix = prefix )
  File "/opt/shed_tools/central/toolshed.g2.bx.psu.edu/repos/iuc/gatk2/f760c0de8e3a/gatk2/gatk2_wrapper.py", line 29, in gatk_filename_from_galaxy
    os.symlink( galaxy_filename, gatk_filename )
OSError: [Errno 17] File exists